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School of Veterinary and Biomedical Sciences, Murdoch University, Murdoch, Western Australia 6150, Australia
Correspondence
David J. Hampson
d.hampson{at}murdoch.edu.au
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and Serpulina murdochii Stanton et al. 1997 in the genus Brachyspira, as Brachyspira intermedia comb. nov. (type strain ATCC 51140T) and Brachyspira murdochii comb. nov. (type strain ATCC 51284T).
The GenBank/EMBL/DDBJ accession numbers for the 16S rRNA gene sequences of Brachyspira intermedia ATCC 51140T and Brachyspira murdochii ATCC 51284T are U23033 and AY312492, respectively.
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). Currently, the two main genera of clinical interest are Brachyspira and Serpulina, as they include pathogenic as well as commensal species. The genus Brachyspira, originally containing the single species Brachyspira aalborgi, was proposed in 1982 (Hovind-Hougen et al., 1982). B. aalborgi colonizes humans and its pathogenicity remains uncertain. The genus Serpulina, containing the species Serpulina hyodysenteriae and Serpulina innocens, was proposed by Stanton (1992). These two species colonize pigs and were originally allocated to the genus Treponema as Treponema hyodysenteriae, the agent of swine dysentery (Harris et al., 1972), and the non-pathogenic Treponema innocens (Kinyon & Harris, 1979). Subsequently, both species were transferred briefly to the proposed new genus Serpula (Stanton et al., 1991). Because this genus name was discovered to be illegitimate due to the prior existence of the fungal genus Serpula, both species were then reclassified in the new genus Serpulina. A third Serpulina species, Serpulina pilosicoli, was proposed in 1996 (Trott et al., 1996b). S. pilosicoli was pathogenic to pigs and chickens and colonized humans and many species of animals and birds. Subsequently, it was proposed that the genera Serpulina and Brachyspira be unified and that S. hyodysenteriae, S. innocens and S. pilosicoli be transferred to the genus Brachyspira, as Brachyspira hyodysenteriae comb. nov., Brachyspira innocens comb. nov. and Brachyspira pilosicoli comb. nov. (Ochiai et al., 1997). These new name combinations appeared in Validation List no. 64 (Ochiai et al., 1998). Concurrently, a description of the novel species Serpulina alvinipulli was published, with the updated name Brachyspira alvinipulli added in proof in response to the transfer of the three other former Serpulina species to the genus Brachyspira (Stanton et al., 1998). Two further Serpulina species, Serpulina intermedia and Serpulina murdochii, were proposed in 1997 (Stanton et al., 1997). Unfortunately, due to the timing of their description, they were not included in the transfer of species when the genera Serpulina and Brachyspira were unified in 1997. This situation has since been a source of some confusion, with various authors now pragmatically electing to call the two remaining Serpulina species ‘Brachyspira intermedia’ and ‘Brachyspira murdochii’, respectively, rather than the validly published names S. intermedia and S. murdochii.
The current paper proposes the transfer of S. intermedia and S. murdochii to the genus Brachyspira. In support of this proposal, published data relating to the five current Brachyspira species and the two Serpulina species (Stanton et al., 1991, 1996, 1997, 1998; Ochiai et al., 1997) were reassessed. All seven species are slow-growing anaerobic spirochaetes that colonize the distal intestinal tract. All seven have a low G+C content, with values for the type strains of the species varying in the range 24.6 mol% for B. alvinipulli ATCC 51933T (Stanton et al., 1998) to 27.1 mol% for B. aalborgi NTCC 11492T (Ochiai et al., 1997). S. intermedia ATCC 51140T has a G+C content of 25 mol% and S. murdochii ATCC 51284T a G+C content of 27 mol% (Stanton et al., 1997). In a study using multilocus enzyme electrophoresis (MLEE) and partial sequencing of the 16S rRNA gene to analyse strains of the seven intestinal spirochaete species, these species were clustered together, with B. aalborgi being the most distantly related of the species (Stanton et al., 1996). These results are consistent with the two Serpulina species belonging to the same genus as the Brachyspira species. To illustrate these relationships, partial (1205 bp) 16S rRNA gene sequences of the seven type strains were obtained from the DDBJ/GenBank/EMBL databases and used to create a dendrogram (Fig. 1). Again, B. aalborgi appears as the outlying species. Pairwise alignments of these sequences for the seven type strains gave similarity values in the range 95.5–99.7 %, consistent with the species belonging to the same genus (Ochiai et al., 1997). S. intermedia ATCC 51140T was most closely related to B. hyodysenteriae ATCC 27164T (99.7 % similarity), whereas S. murdochii was most closely related to B. innocens ATCC 29796T (99.4 % similarity).
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) and are reiterated. B. hyodysenteriae is the species most closely related to S. intermedia. Besides their almost identical 16S rRNA gene sequences, DNA from the type strains of B. hyodysenteriae and S. intermedia showed 57–68 % relative reassociation (Stanton et al., 1997), closely approaching the value of 70 % that is usually used to indicate that two strains belong to the same species (Wayne et al., 1987). Furthermore, they share a number of phenotypic properties: both produce indole and typically have 
-glucosidase and 
-glucosidase activity when tested in the commercial API ZYM system (Lee et al., 1993; Fellström & Gunnarsson, 1995). However, the two species can be distinguished by MLEE analysis (Stanton et al., 1996) and on the basis of consistent differences in the sequences of their 23S rRNA genes (Leser et al., 1997) and their NADH oxidase genes (Atyeo et al., 1999). A notable feature of B. hyodysenteriae is that it produces a strong -haemolysis on blood agar, whereas S. intermedia produces weak haemolysis. Infection of the porcine colon with B. hyodysenteriae induces a severe mucohaemorrhagic diarrhoea (swine dysentery), whereas S. intermedia is generally not considered to be pathogenic in pigs (Harris et al., 1999). Hence the two species have clear phenotypic and biological differences that can be used to differentiate them.
The second Serpulina species, S. murdochii, is most closely related to B. innocens. These two species have very similar 16S rRNA gene sequences and the type strains have 64–66 % DNA–DNA relative reassociation (Stanton et al., 1997), which again is borderline in terms of differentiating species (Wayne et al., 1987). However, they clearly cluster in different groups in MLEE analysis (Stanton et al., 1996; McLaren et al., 1997) and can be separated on the basis of differences in their NADH oxidase gene sequences (Atyeo et al., 1999) and by restriction fragment length polymorphism analysis of PCR-generated 16S rRNA gene products (Stanton et al., 1998). They also have minor phenotypic differences, with B. innocens typically being -galactosidase-positive whereas S. murdochii is typically negative for this activity (Lee et al., 1993; Fellström & Gunnarsson, 1995). These differences are sufficient to allow them to be distinguished as separate species.
Taken together, these data demonstrate that the seven named species of anaerobic intestinal spirochaetes are distinct, but are closely related, and that it is appropriate that they be unified in a single genus. The genus name Brachyspira has chronological precedence over the name Serpulina and hence all seven species should be located in the genus Brachyspira. Therefore, we propose the transfer of Serpulina intermedia and Serpulina murdochii to the genus Brachyspira, as Brachyspira intermedia comb. nov. (type strain ATCC 51140T) and Brachyspira murdochii comb. nov. (type strain ATCC 51284T).
Description of Brachyspira intermedia comb. nov.
Brachyspira intermedia [in.ter.me'di.a. L. fem. adj. intermedia that is between, intermediate, referring to the fact that the biochemical reactivities of this organism are intermediate between those characteristically possessed by B. hyodysenteriae and by B. innocens (Lee et al., 1993)].
Basonym: Serpulina intermedia Stanton et al. 1997.
Previously also known as ‘Serpulina intermedius’ (Lee et al., 1993). Some intestinal spirochaetes referred to as ‘Treponema hyodysenteriae’ biotype 2 or ‘intermediate type’ may be B. intermedia strains (Binek & Szynkiewicz, 1984).
B. intermedia strains have been isolated from commercial poultry flocks exhibiting diarrhoea and reduced production (McLaren et al., 1997; Stephens et al., 2005), and experimental infection of laying hens with a pure culture of a B. intermedia strain has caused reduced egg production and increased faecal water content (Hampson & McLaren, 1999). The description is as given previously by Stanton et al. (1997).
The type strain is ATCC 51140T (=CIP 105833T).
Description of Brachyspira murdochii comb. nov.
Brachyspira murdochii (mur.do'chi.i. N.L. masc. gen. n. murdochii of Murdoch, in recognition of work conducted at Murdoch University in Western Australia, where the type strain was identified).
Basonym: Serpulina murdochii Stanton et al. 1997.
Previously known as ‘group B spirochaetes' and S. murdochii (Lee et al., 1993; Lee & Hampson, 1994). B. murdochii strains have been isolated from the large intestinal contents of healthy swine and rats (Trott et al., 1996a) and from chickens (Stephens et al., 2005). The spirochaete generally is not considered to be a pathogen, although occasionally it has been seen in association with colitis in pigs (Weissenbock et al., 2005). The description is as given previously by Stanton et al. (1997).
The type strain is ATCC 51284T (=CIP 105832T=DSM 12563T).
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REFERENCES |
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